1. Field of the Invention
The present invention relates to a semiconductor fabricating apparatus including a maintenance monitor that determines the timing of performing the maintenance of a semiconductor processing chamber.
2. Description of the Related Art
A semiconductor fabricating apparatus is a very delicate machine. If the state of a processing chamber in which wafers are processed varies, the characteristics of semiconductors vary greatly. For example, in a plasma-processing apparatus, a material in a chamber, which is etched or removed through etching or sputtering may generate an abnormal electric discharge. Raw gas or a reactive product deposited in the chamber may generate particles to degrade a process yield.
Consequently, for plasma processing, performed as one semiconductor fabricating process, after a predetermined number of wafers has been processed, a plasma-processing chamber is left open in order to perform maintenance work that includes exchanging parts and wet cleaning. Conventionally, semiconductor memories, such as DRAMs, are fabricated through mass production. The maintenance timing is therefore determined experimentally. Moreover, sampling inspection may be performed on processed wafers in order to check if the uniformity in handling wafers fluctuates during one process, or a particle monitor may be used for measurement. Based on the result of the check or measurement, the timing of parts exchange or cleaning may be determined (refer to, for example, Japanese Unexamined Patent Application Publication No. 2001-59808).
However, limited production of diversified products has come to be adopted more frequently in recent years. The frequency of performing different processes in the same processing chamber is also higher. If a kind of product differs from lot to lot, it is hard to determine the timing for performing maintenance work. If maintenance is performed because of process condition fluctuation or particle generation, or if maintenance is performed in an early stage with a large margin preserved, unnecessary costs will occur.
Japanese Unexamined Patent Application Publication No. 2002-261001 has disclosed a technology that measures a degree of contamination by making the most of the fact that the frequency of oscillation of a crystal oscillator changes due to a contaminant film formed on the crystal oscillator. However, it is hard to use the crystal oscillator in an environment for plasma processing of semiconductor fabricating process. Moreover, the crystal oscillator is suitable for detection of a minute change that is of the level of a change in the thickness of a molecular film. However, the crystal oscillator is unsuitable for detection of a change in the thickness of a film, which is several micrometers or more, occurring during etching of an oxide or during forming of a layer.